This invention relates to an aircraft takeoff monitor and relates more particularly to the method and means for displaying the aircraft takeoff and stopping status to the aircraft pilot. The apparatus and method are supplements to existing onboard monitors.
Several monitoring systems, devices, and techniques are currently disclosed to monitor the performance of an airplane during takeoff. However, they generally involve complicated sensing devices, a multiplicity of computing elements, and/or elaborate visual displays, all combining to yield devices which only add to the cockpit confusion during takeoff. The prior art devices do not provide the pilot with a simple, easy to read indication of when the aircraft is not performing as predicted. None of the prior art devices indicate how the rate at which the takeoff conditions are deteriorating nor the rate at which the aircraft is running out of stopping distance on a given runway.
U.S. Pat. No. 3,048,329 to L. E. Berggren discloses the typical orientation of most of the prior art devices. This patent discloses a cockpit instrument panel which tells the pilot where his aircraft is with respect to a point designated as a point of no return. When submarginal acceleration is experienced, the instrument panel automatically results in an abort signal, if the aircraft is not past the point of no return. If the actual acceleration is less than a selected minimum, the abort signal is generated provided that the distance measured from the end of the runway is not greater than that computed for the point of no return. There is no simple indicator indicating how close the aircraft would stop to the end of the runway if the brakes were applied.
U.S. Pat. No. 3,205,707 to H. K. Richter also discloses a performance monitor, but the Richter device is designed for a particular aircraft and does not incorporate a means for adjusting for a number of takeoff variables, except altitude. An altitude compensator, forming a part of the performance meter, automatically adjusts the device via a variable potentiometer, for takeoff pressure conditions actually existing at the time.
U.S. Pat. No. 3,368,065 issued to E. R. Kendall discloses an aircraft instrument which indicates (1) the actual distance traveled during the ground run, and (2) the extra distance that needs to be traveled to attain a velocity increase. The pilot is thereby provided with a visual indication of the acceleration performance of the aircraft and can thus detect when it is subnormal. However, nothing indicates how rapidly conditions are deteriorating. The Kendall specification discloses a rather complex four region display area with an index driven across it to show progress along the runway.
Nearly all of the prior art devices focus on a calculated air speed (V.sub.l). Below this speed, a multi-engined aircraft may be safely stopped on the remaining runway, but cannot safely continue takeoff if an engine fails. Above this speed, the takeoff is committed, no stop is possible, but if an engine fails, the airplane can safely become airborne. This V1 speed is determined from FAA required data provided by the airplane manufacturer. It must be determined for each individual takeoff, based on the specific conditions existing at the time of takeoff. The Vl speed depends on the following variables: airplane weight, runway altitude, runway length, runway gradient, air temperature, and the wind velocity component in the direction of takeoff.
There is a serious deficiency, however, in this manner of operation. The reliance on Vl for takeoff safety is based upon "normal" performance of the airplane. Usually this is the minimum performance that can be expected, so there is some margin for error most of the time. If this margin becomes negative and an engine failure occurs, an accident can be expected.
In present practice with the existing takeoff monitoring devices, the pilot has the option of aborting a takeoff at any time the air speed is below the Vl speed determined for that particular takeoff. This is supposed to assure that there is sufficient runway to stop. However, this is only true if the airplane started the takeoff at the prescribed place on a runway, and the airplane performs "normally" for the entire time of the takeoff. If there is a slight performance degradation and Vl is not reached, it is probable that a takeoff can continue, but there is no assurance that the airplane can be stopped on the remaining runway. In extreme cases, where performance is so degraded that the airplane cannot safely become airborne, there is obviously no possibility of stopping if the takeoff run is continued too far in an attempt to reach V1.
The assumption that the airplane can be stopped on the runway at any speed below V1 is erroneous and dangerous because it is only true for a "normal" takeoff. For an "abnormal" takeoff, there is no assurance that the plane can be stopped on a runway, even though the air speed is below V1.
The present invention provides additional information to the crew to help them assure safety during the entire takeoff. With this additional information, they can then determine whether the airplane is proceeding "normally" along the takeoff path and whether there is sufficient runway left to stop. The invention actually indicates when the airplane is not performing "normally" and how far behind a "normal" takeoff the airplane actually is. The rate of change of the display indicates how rapidly the aircraft is falling behind.
The present invention thus provides the information needed by the crew to make an informed decision, requiring the least amount of interpretation, and in the shortest possible time. It does this by displaying to the crew the takeoff and stopping status at all times from the start of the takeoff until lift-off. The takeoff status display shows continuously how many feet, if any, the airplane is behind "normal" takeoff distance. The stopping status display of the present invention shows how many feet of runway would remain (stopping margin), if the takeoff were aborted with less than some arbitrary margin, say 1,000 feet. This, in effect, gives an anticipatory warning that the possibility of stopping on the runway will soon be passed. The present invention further provides a flashing display signal when the aircraft cannot be stopped on the remaining runway length.